Quantitative NMR investigation on the low-temperature dissolution mechanism of chitin in NaOH/urea aqueous solution
Quantitative NMR investigation on the low-temperature dissolution mechanism of chitin in NaOH/urea aqueous solution
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DOI：
10.1007/s10570-015-0667-2
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发表时间：
2015-05
期刊：
影响因子：
5.7
通讯作者：
Geying Ru;Huan Luo;Xinmiao Liang;Liying Wang;Chaoyang Liu;Jiwen Feng
中科院分区：
文献类型：
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作者：
Geying Ru;Huan Luo;Xinmiao Liang;Liying Wang;Chaoyang Liu;Jiwen Feng
甲壳素在氢氧化钠/尿素水溶液中的低温溶解机理尚未完全确定，尤其是在降低氢氧化钠和尿素结晶温度的情况下。用多核(1H、15N和23Na)核磁共振方法发现，与完全冻结的二元NaOH-D2O体系不同，三元体系在−40°C以下存在固-液共存，在−40°C时残留的液相由一定浓度的NaOH(10wt%)、尿素(13wt%)和D2O组成。我们的核磁共振结果进一步证明，甲壳素在低温(−40和−70°C)下溶解在残留液体相(含5-10wt%NaOH和8-12wt%尿素)。尿素的一个重要作用是提高了氢氧化钠水溶液的低温稳定性，从而增加了甲壳素的溶解温度范围，从而为甲壳素的溶解提供了必要的低温液体环境。
The low-temperature dissolution mechanism of chitin in NaOH/urea aqueous solution has not been well established yet, especially at a temperature that lowers the crystallization temperature of both NaOH and urea. Using multiple nuclei (1H,15N and23Na) nuclear magnetic resonance (NMR) methods, we find that the ternary NaOH/urea/D2O system, different from the fully frozen binary NaOH–D2O system, exhibits solid-liquid phase coexistence below −40 °C, and the residual liquid phase consists of certain concentrations of NaOH (10 wt%), urea (13 wt%) and D2O at −40 °C. Our NMR results further demonstrate that chitin dissolves in the residual liquid phase (containing 5–10 wt% NaOH and 8–12 wt% urea) at low temperatures (−40 and −70 °C). An important role of urea is enhancing the low-temperature stability of NaOH aqueous solutions and then increasing the dissolution temperature range of chitin, thus providing an essential low-temperature liquid environment for chitin dissolution.